How it affects your account goal if you add or remove a campaign, depends on the set goal.
If you have selected Autopilot, it has no impact on existing campaigns.
However, if costs/month is set as goal, costs will also be apportioned to the newly added campaign. Therefore, the expenses for other campaigns are less to achieve the set goal.
If you remove a campaign, it is exactly the opposite. Then there are fewer campaigns that contribute to the costs. That’s why the expenses for each campaign need to be higher to achieve the overall account goal.
3. Cost/conversion, ROI, CRR
If you have chosen one of these goals, a big impact will only be expected if the added or removed campaign has a significantly different goal compared to the existing campaigns.
Example: You have set a ROI target and add a new campaign, for which it is much easier to achieve a high ROI compared to the other campaigns. Then there will be a shift of advertising spending to the new campaign to make use of this favorable situation.